At the quarter post of the season, the Green Bay Packers rank last in the NFL in run defense.

Now, the NFL is a bottom-line business, and the Packers beat the Chicago Bears on Sunday. So that and their 2-2 record matter most.

But their run defense blew up against a Bears team that had struggled running the ball its first three games. And the Packers' problems stopping the run through four games are a big issue going forward. You can't challenge for championships with one of the worst run defenses in the game.

It's natural to question whether the Packers' run-stopping woes go back to the changes on the defensive line and scheme in the offseason. They didn't bring back Ryan Pickett and Johnny Jolly, and they lost B.J. Raji during training camp to a season-ending biceps injury. All three were in the range of 330 pounds or more. The Packers now have a smaller, quicker defensive line.

But good run defense doesn't require a huge defensive line, and a huge defensive line doesn't guarantee good run defense. Last year, the Packers were among the league's lowest-rated run defenses (No. 25 in yards allowed per game and No. 29 in yards allowed per carry) with Pickett, Raji and Jolly playing regularly.

And this season, the Seattle Seahawks are one the NFL's best run defenses (Nos. 5 and 1, respectively) even though they don't have any behemoths. Their defensive tackles range from 303 pounds to 313 pounds. Defensive linemen that size still can play good or even great run defense, but they have to play strong and be disciplined within the scheme.

You have to think the Packers' defensive coaches and players were appalled when they looked at the final stat sheet Sunday and saw they gave up 496 total yards to the Bears, including 235 rushing. Time and again, halfbacks Matt Forte (122 yards on 23 carries) and Ka'Deem Carey (72 yards on 14 carries) slashed through their defense for nice gains. And it's not like one or two big runs distorted the numbers. The Bears' long rush was only 19 yards.

To accommodate their smaller and quicker linemen, the Packers are operating in a new gap-attacking run defense, as opposed to the two-gap, read-and-react scheme coordinator Dom Capers had used from 2009 through last season. Watching the videotape from Sunday, one thing stood out: The Packers too often were undisciplined or out of control in the trenches against the run.

Defensive lineman Letroy Guion, for instance, got too far upfield on several occasions that helped turn short runs into medium gains. It happened a couple of times in the first quarter alone.

For instance, on the first drive, the Bears on second-and-11 from the Packers' 15 gave the ball to Forte up the middle. The Packers were in their nickel personnel, with Guion and Mike Daniels at the defensive tackles.

Guion got into his gap between center Brian de la Puente and right guard Kyle Long, but rather than sit in the gap, as he's supposed to, he blasted through and created a big lane for Forte. At the same time, Daniels tried to go underneath de la Puente's block. He's quick enough to get away with it sometimes, but not on this play. So Forte bolted through the big opening for 6 yards, creating a manageable third-and-5, on a play that should have gone for only 3.

Later, on a first down with 3:26 left in the first quarter, the Packers again were in their nickel. The Bears ran a similar play, and Guion did the same thing. If he'd sat in his gap and tried to squeeze it, Forte wouldn't have had much if any running lane. Instead, Forte shot through the huge hole and bowled over safety Morgan Burnett for a 7-yard gain that set up a highly favorable down-and-distance, second-and-3.

The same applied to outside linebacker Clay Matthews on a snap or two. Matthews is the Packers' best defensive player, and maybe this is simply the price the Packers have to pay for his playmaking as a pass rusher. But his aggressiveness going after the quarterback occasionally helps running backs pick up nice gains.

That happened on the game's second play Sunday. The tight end lined up across from him, Dante Rosario, released on an apparent pass route, so Matthews bolted on a rush. But the play was a handoff to Forte up the middle. When Matthews saw the handoff, he was a little too far upfield to crash inside and make the tackle. Forte picked up 8 yards and a first down.

So what's the answer to the Packers' run-stopping problems? Maybe they'll adjust better to the new one-gap scheme as the season goes on. Or maybe undrafted rookie Mike Pennel, who at 332 pounds is their heaviest player, will improve the more he plays.

Pennel looked good in the preseason at nose tackle, where he lines up only inches from the center and things happen fast. He didn't look so good in his NFL debut Sunday while playing 22 snaps, mainly in the nickel at defensive tackle. Things happen a half-beat slower there than at nose, and Pennel looked mechanical, like he was waiting for something to happen. Kind of like Josh Boyd for much of his rookie season last year.

Pennel did have a good bull rush on Matthews' interception in the third quarter. He's a big, powerful player, so maybe with more playing time, he'll start to make a difference.

SECONDARY MATTERS

The Packers' playmaking in the secondary early this season is reminiscent of 2010, when it also was the team's best defensive position group.

Against the Bears, cornerbacks Tramon Williams and Sam Shields made big plays, just as they did during the Packers' Super Bowl run in '10. Williams in the third quarter Sunday jumped the slant route and made the deflection that Matthews intercepted. Shields later in the third quarter reacted fast to the throw on a misread between quarterback Jay Cutler and receiver Brandon Marshall for the interception that basically clinched the game.

Also, almost every week first-round pick Ha Ha Clinton-Dix looks more and more like a player. The safety made the biggest play of the game when he pulled tight end Martellus Bennett from the brink of a touchdown on the final play of the first half. Can you imagine M.D. Jennings or Jerron McMillian making that play last year?

Clinton-Dix is a complete safety and fills fast on run defense as well. On one illustrative play in the second quarter, Cutler from the shotgun formation handed off to Forte up the middle. Clinton-Dix read it early, burst from his deep safety position and met Forte at the line of scrimmage. Forte had room to jump cut to his left and avoid the hit, but that sent him straight at linebacker Jamari Lattimore, who tackled Forte for only a 2-yard gain.

Former football coach and player Eric Baranczyk offers his analysis of Green Bay Packers games each week.

— pdougher@pressgazettemedia.com and follow him on Twitter @PeteDougherty